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Abstract: This paper describes 20th century climate and human impacts on terrestrial and fluvial systems in the Dabie Mountains, Anhui Province, China, based on analyses of four types of information. Analyses of particle size, mineral magnetism, organic carbon, nitrogen and phosphorus in a sediment core taken from the Longhekou reservoir, built in 1958 AD in the upper reaches of Hangbu River, provide an ∼45 year record of fluvial responses, while monitored meteorological and hydrological data provide records of climate and river discharge. Census data compiled for the local Shucheng County provide records of population and land use, complemented with analyses of satellite images. The Xiaotian river delivers over 65% of the total water and silt to the reservoir. Analyses indicate that the fluvial regime tracks the monsoon climate over seasonal timescales, but human activities have a strongly mediating effect on sediment supply, sediment delivery and, to a lesser extent, runoff over longer timescales. Notable periods of human impact on erosion include the Great Leap Forward (1958–1960) and Great Cultural Revolution (1966–1976). A rising trend in precipitation and new land use changes at the present time may be leading to an enhanced flood risk. [Copyright &y& Elsevier]

Regions around Dabie Mountain (DBM) in the Yangtze River basin (YRB) are the source of a mesoscale vortex: the Dabie vortex (DBV). Based on a 14-yr statistical study, 11 long-lived heavy-rain-producing DBVs were composited for convection-permitting semi-idealized simulations. A control simulation, initialized 12 h before the composite vortex formation, successfully reproduced a DBV, with all the salient characteristics of the 11 events. Sensitivity experiments were designed to understand the impacts of large-scale environmental conditions, regional topography, and latent heating on DBV formation. The main results were as follows: (i) Supposition of a 500-hPa shortwave trough with an east–west-oriented lower-level transversal trough around the DBM is crucial for the formation of vortices. A nocturnal lower-level jet on the southern side of the transversal trough accelerates DBV formation by enhancing convergence, triggering/sustaining convection, and producing cyclonic vorticity. (ii) During the simulation period, the topography east of the second-step mountain ranges, including the DBM, significantly affects nearby precipitation and convective activity, whereas this is not crucial for DBV formation. (iii) Latent heating is not required for generating DBVs, but it enhances the intensity, longevity, and eastward progression of these vortices along the shear line associated with the transversal trough. (iv) The vorticity budget suggests the convergence-related (horizontal) shrinking and vertical transport dominate the cyclonic-vorticity increase associated with DBVs, whereas tilting and horizontal transport mainly act in the opposite manner. [ABSTRACT FROM AUTHOR]

Two eclogites, one from the southern Dabie Shan, China, and the other from the western Erzgebirge, Germany, were studied because of amphibole and clinozoisite–epidote formation either as typical porphyroblasts or as oriented fine-grained matrix minerals. A nearly isobaric prograde path was derived for the eclogite from the Erzgebirge, mainly on the basis of garnet zonation and the reconstruction of P–T pseudosections in the system SiO2–TiO2–Al2O3–MgO–MnO–FeO–CaO–Na2O–K2O–H2O–O2. Peak P–T conditions were 2·8 GPa and 670°C. The retrograde path shows significant cooling during pressure release. In contrast, the Dabie Shan eclogite contains sparse Mg-rich garnet cores pointing to a granulite stage. Subsequently, peak-pressure conditions of 3·5–4·0 GPa were reached at 620°C, followed by a retrograde path that was initially nearly isothermal and then similar to that of the Erzgebirge eclogite. Most of the amphibole and clinozoisite–epidote grew during early retrogression in the pressure interval 1·8–2·3 GPa (Erzgebirge) or 2·4–2·7 GPa (Dabie Shan) owing to infiltration of hydrous fluids amounting to ∼1 wt % and 0·5 wt % H2O, respectively. As a result of this hydration omphacite was partially decomposed, but the remaining omphacite demonstrates that infiltration of H2O essentially ceased at 1·8 GPa (Erzgebirge) or 2·4 GPa (Dabie Shan). The fluid infiltration and hence the growth of amphibole and clinozoisite–epidote is proposed to have occurred in a deep-seated subduction channel during ascent of eclogitic material. Subsequently, the eclogites were captured between colliding continental plates and further exhumed in an exhumation channel. [ABSTRACT FROM AUTHOR]

The water vapor budget and the cloud microphysical processes associated with a heavy rainfall system in the Dabie Mountain area in June 2008 were analyzed using mesoscale reanalysis data (grid resolution 0.03° × 0.03°, 22 vertical layers, 1-h intervals), generated by amalgamating the local analysis and prediction system (LAPS). The contribution of each term in the water vapor budget formula to precipitation was evaluated. The characteristics of water vapor budget and water substances in various phase states were evaluated and their differences in heavy and weak rainfall areas were compared. The precipitation calculated from the total water vapor budget accounted for 77% of actual precipitation; surface evaporation is another important source of water vapor. Water vapor within the domain of interest mainly came from the lower level along the southern boundary and the lower-middle level along the western boundary. This altitude difference for water vapor flux was caused by different weather systems. The decrease of local water vapor in the middle-lower layer in the troposphere during the system development stage also contributed to precipitation. The strength and the layer thickness of water vapor convergence and the content of various water substances in the heavy rainfall areas were obviously larger than in the weak rainfall areas. The peak values of lower-level water vapor convergence, local water vapor income, and the concentration of cloud ice all preceded the heaviest surface rainfall by a few hours. [ABSTRACT FROM AUTHOR]

The partial breakdown of Ti-chondrodite and Ti-clinohumite during exhumation from ultra-high pressure to amphibolite facies conditions in garnet-pyroxenites from Dabie Shan (China) produces coronas of olivine coexisting with ilmenite blebs. Fourier transform infrared (FTIR) spectra of this newly formed olivine exhibit absorption bands in the hydroxyl-stretching region. Two intense peaks were observed at 3,564 and 3,394 cm−1, identical in energy to peaks in Ti-clinohumite. Transmission electron microscopy (TEM) of the same olivine domains revealed the presence of a complex (001) planar intergrowth. These interlayers have a 1.35 nm repeat distance, which is characteristic of clinohumite. Such interlayers are also enriched in Ti with respect to the adjacent olivine as shown by energy dispersive spectrometry. The combined evidence from FTIR spectroscopy and TEM indicates that OH is incorporated along Ti-clinohumite planar defects. This study provides evidence that the nominally anhydrous phase olivine may contain OH as a humite-type defect beyond the breakdown of the hydrous humite minerals and confirms earlier suggestions that Ti plays a key role in OH incorporation in mantle olivine. We suggest that olivine containing Ti-clinohumite defects is an important phase for water transport in subduction zones and for the storage of water in cold subcontinental mantle. However, these defects are unlikely to be stable in hotter parts of the oceanic mantle such as where basaltic magmas are generated. [ABSTRACT FROM AUTHOR]

Fluid inclusions may provide compositional and isotopic information about fluids from which the host mineral precipitated as long as the host mineral does not react with the fluid. Our transmission electron microscope (TEM) investigation of grain boundaries and of fluid inclusions in zoisite and quartz of high-pressure metamorphic rocks from Dabie Shan (eastern China) demonstrates daughter minerals, such as margarite, muscovite, calcite, and anhydrite. Their precipitation changes (1) the composition of the fluid by selective and mineral-specific removal of CO2 (carbonates), H2O (sheet silicates, hydration of the walls), or S (gypsum, anhydrite, sulfides), (2) the concentrations and proportions of ions dissolved in the fluid, and (3) the isotopic composition of the fluid because of isotopic fractionation between mineral precipitate and fluid and between unmixed fluids. Fluid leakage from overpressurized fluid inclusions with daughter minerals changes the overall chemical and isotopic composition of the inclusion irreversibly, even when the daughter crystals later redissolve. Such fluid loss yields a wide range of compositionally and isotopically different fluids from a single starting fluid. Depending on the relation between mineral reactions in and fluid loss from the inclusion, the fluid remaining in the inclusion and the fluid lost from the inclusion may appear entirely unrelated. [ABSTRACT FROM AUTHOR]